Complex fertilizers of potassium tripolyphosphate base



State 6 Claims. 01. 71 s1 This application is a division of ourcopending application, Serial No. 105,300, filed April 25, 1961, nowPatent No. 3,193,374. This invention relates to complex fertilizershaving a base of potassium tripolyphosphate and containing the threefertilizing elements, nitrogen, potassium and phosphorous.

It is known that one may produce from compositions of phosphoric acidcomplete fertilizers containing these three elements, but that suchfertilizers have heretofore scarcely exceeded 60% of them.

It is also known that potassium tripolyphosphate constitutes afertilizer having a high content of K and P 0 and that of the total 100%of fertilizing elements 52.5% is K 0 and 47.5% is P 0 when thefertilizer is prepared from pure phosphoric acid, and that thisfertilizer is substantially totally soluble in natural water. At thesame time the use of such fertilizer is difiicult, if not impossible,because of its great hygroscopicity which causes it to lump togetherduring storage.

It is an object of this invention to make new fertilizers containing thethree elements N, P and K which contain at least 75% of fertilizingelements and being highly soluble in water while at the same timelacking hygroscopicity. These new products have been made by the processhereinafter described.

In the preferred form of the invention the potassium tripolyphosphateused in the preparation of the fertilizer should be made from phosphoricacid which has itself been made by the Wet way, and which mayadvantageously contain trace elements as impurities such as magnesium,copper and manganese which are beneficial to the soil in small amounts.The potassium tripolyphosphate is advantageously prepared by adding tophosphoric acid some potassium carbonate or, preferably, potassiumhydroxide in concentrated solution, the proportions being such as toestablish the ratio of potassium to phosphorous of 5 to 3. The fixing ofthis ratio may advantageously be precise and can be established by theuse of a pH meter, the solution of potassium hydroxide being added tothe phosphoric acid until the pH reaches 6.8 at which level the additionceases. The solution thus prepared is dried, the product obtained bydrying is put in a furnace at 200 C. for /2 hour, and thereafter thetemperature is raised to 400 C. for 1 hour to produce the condensationto tripolyphosphate. The tripolyphosphate drawn from the furnacecontains much higher, insoluble polyphosphates detectable bychromatographic analysis and has the following approximate composition:

Percent P 0 total 46.2 Water soluble P 0 44.5

Water soluble K 0 47.2

This potassium tripolyphosphate is hygroscopic and contains 93.4% offertilizing elements of which 91.7% are soluble in water.

In preparing the new product the potassium tripolyphosphate abovedescribed is moistened with phosphoric acid of medium concentration, forinstance containing about 30% P 0 and is granulated by the methods whichate t 3,218,150 Patented Now-16, 1965 Percent Total P205 Water soluble P0 41.9 Water soluble K 0 33 Ammoniacal nitrogen 2.9

constituting a total of 78.5% of fertilizing elements of which 77.8% aresoluble in water. Consequently this fertilizer contains the threefertilizing elements in very high percentage.

If it is desired to still further increase the content of nitrogen onemay add to this fertilizer a fertilizer having high nitrogen contentsuch as urea or diammonium phosphate. The operation is carried out asdescribed above, that is to say potassium tripolyphosphate is mixedwiththe selected nitrogenous fertilizer, the mixture is moistened withphosphoric acid and the granulator is supplied with a slow current ofammonia. There is thus produced a complex fertilizer which is nothygroscopic and which contains 83% to 88% of fertilizing elements ofwhich a very high proportion is soluble in water.

The following examples also illustrate the invention:

Example A To 52 parts of potassium tripolyphosphate by weight containing52.5% K 0 and 47.5% P 0 there are added 43 parts of diammonium phosphatehaving a ratio of N to P about 1.5. The mixture is moistened with 10parts of phosphoric acid containing 30% P 0 by weight and granulation iscarried out in the usual apparatus and under the usual conditions in thepresence of an atmosphere containing a substantial proportion ofammonia, 1.7 parts by weight of nitrogen were fixed as NH (2.07 parts NHin the ammoniation step. The fertilizer thus obtained has thecomposition:

Percent Total P 0 51.2 Water soluble P 0 50.7 Assimilable P 0 51 Watersoluble K 0 27 Ammoniacal nitrogen 8.8

This adds up to a total of 87% of fertilizing elements of which 86.5%are water soluble. The fertilizer was granular, and contained 8.8% ofammoniacal nitrogen, 51.2% anhydrous P 0 and 27% anhydrous K 0.

Example B Mix 76 parts of potassium tripolyphosphate containing 52.5% K0 and 47.5% P 0 and 20 parts of urea, in place of ammonium phosphate,then proceed as in Example A using 21.5 parts of phosphoric acidcontaining 30% P 0 1.2 parts of ammonia were fixed from an ammoniaatmosphere in the granulator. The fertilizer obtained contains:

Percent TOtal P205 Water soluble P 0 37.4 Assimilable P 0 37.8 Watersoluble K 0 36 Total nitrogen 9.4

This adds up to 83.6% of fertilizing elements of which 82.8% are watersoluble.

Field tests have been made following the methods of Neubauer and the newproducts have been tested for absorption by barley plants. In comparisonto barley plants treated by the classical fertilizers, calcium nitrate,

superphosphate, and potassium chloride, the new fertilizers showedexcellent assimilability of the P and the K 0 and provided by thepotassium tripolyphosphate, the assimilability of phosphorous andpotassium being the same for the new products as for the fertilizers ofsuperphosphate and potassium chloride, when used in equal quantities andstandard doses. The new fertilizers may be used in all spring and fallplantings either by incorporation in the soil, by pulverization withmulch or in water of irrigation.

These products are much superior to those prior art fertilizers madefrom phosphoric acid which were complete in N, P and K, particularly inthat they contain a much higher content of the three elements, being onthe order of 75% or more as compared to the approximate maximum of 60%attained by the prior art product.

As many apparently Widely different embodiments of the present inventionmay be made without departing from the spirit and scope thereof, it isto be understood that the invention is not limited to the specificembodiments.

What is claimed is:

1. A granulated non-hygroscopic fertilizer containing tripolyphosphateof potassium and ammoniacal nitrogen, in which water soluble P 0 and K 0are present in major amounts, up to about 51% P 0 and 36% K 0 by weight,and N is present in a minor amount and in which more than 60% of theelements P, K and N are in a form assimilable by plants and soluble inwater.

2. A granulated non-hygroscopic fertilizer containing tripolyphosphateof potassium and ammoniacal nitrogen in which P 0 and water soluble K 0are present in major amounts, up to about 51% P 0 and 36% water solubleK 0 by weight, and N is present in a minor amount, which issubstantially free of insoluble P 0 and in which more than 75% of theelements P, K and N are in a form assimilable by plants and soluble inwater.

3. A granulated non-hygroscopic fertilizer containing tripolyphosphateof potassium and ammoniacal nitrogen in which P 0 and Water soluble K 0are present in major amounts, P 0 being present in an amount from about38% to about 51% by weight, water soluble K 0 being present in an amountfrom about 27% to about 36% by weight, said fertilizer beingsubstantially free of insolu ble P 0 and substantially more than of theP, K and N being present in a form assimilable by plants and soluble inwater.

4. The fertilizer of claim 3 having by weight percent Percent total P 0About 42.6 Water soluble P 0 About 41.9 water soluble K 0 About 33ammoniacal N About 2.9

5. The fertilizer'of claim 3 having by weight percent Percent total P 0About 51.2 Water soluble P 0 About 50.7 assimilable P 0 About 51 watersoluble K 0 About 27 ammoniacal N About 8.8

6. The fertilizer of claim 3 having by weight percent DONALL H.SYLVESTER, Primary Examiner. ANTHONY SCIAMANNA, Examiner.

1. A GRANULATED NON-HYGROSCOPIC FERTILIZER CONTAINING TRIPOLYPHOSPHATEOF POTASSIUM AND AMMONICAL NITROGEN, IN WHICH WATER SOLUBLE P2O5 AND K2OARE PRESENT IN MAJOR AMOUNTS, UP TO ABOUT 15% P2O5 AND 36% K2O BYWEIGHT, AND N IS PRESENT IN A MINOR AMOUNT AND IN WHICH MORE THAN 60% OFTHE ELEMENTS R, K AND N ARE IN A FORM ASSIMILABLE BY PLANTS AND SOLUBLEIN WATER.